Cone-shaped or conical crushers are imperative crushing machines for a wide variety of uses in aggregate industries and mineral processing industries. Conical crushers have been developed into various structures and types.
International patent publication No. WO2009/065995 (hereinafter called ‘prior art 1’) discloses a typical structure of a cone-shaped crusher which includes a frame having a cavity formed therein, a first crushing blade provided inside the frame, a main shaft eccentrically accommodated in the frame, a truncated cone-shaped crusher head coupled to an outer circumferential surface of the main shaft, a second crushing blade that covers the surface of the crusher head, a top bearing part coupled to an upper end of the main shaft, a lower bearing part coupled to a lower end of the main shaft, and driving means for driving the main shaft into a gyratory movement.
Here, the first crushing blade is spaced apart at a proper distance from the second crushing blade mounted on an outer circumferential surface of the crusher head. Objects to be crushed that are put into the cone-shaped crusher are discharged toward the outside of the machine while being compressed and crushed as the gap between the fixed first crushing blade and the second crushing blade that performs the gyratory movement with the main shaft is reduced, and falling as the gap between the two blades increases in turn.
To meet various sizes of rock being introduced, the crushing gap of prior art 1 can be adjusted by moving the crusher head up or down.
To be more specific, the crusher head is movable in the longitudinal direction of the main shaft and has an internal cylindrical cavity with a small diameter portion and a large diameter portion. In addition, the main shaft is formed to have a small diameter portion and a large diameter portion to be inserted into the internal cavity of the crusher head.
The crusher head can move up and down along the main shaft by adjusting the amount of hydraulic fluid that is injected into a hydraulic space which is formed between the upper surface of the large diameter portion of the main shaft and the bottom surface of the small diameter portion of the crusher head.
In order for the crusher head to be able to move along the main shaft, a certain amount of gap should be present between the inner surface of the crusher head and the outer surface of the main shaft. Therefore, the diameter of the cavity of the crusher head which has a small diameter portion and a large diameter portion is larger than that of the opposing outer surface of the main shaft.
Thus, the crusher head and the main shaft perform the same gyratory movement while crushing objects, but relative rotational motions of the crusher head and the main shaft occur as the gyratory movement proceeds.
In greater detail, each of the small diameter portion and the large diameter portion of the cylindrical cavity of the crusher head has a tendency to rotate relatively to the surface of the small diameter portion and the large diameter portion of the main shaft independently. If the gap between the two small diameter portions of the crusher head and the main shaft equals to the gap between two large diameter portions of the crusher head and the main shaft, the small diameter portion of the crusher head needs to rotate at a faster angular velocity than its larger diameter portion so that the small diameter portion of the crusher head and its large diameter portion can rotate at the same linear velocity.
Since the crusher head is a rigid body, its small diameter portion and large diameter portion are supposed to rotate at a single angular velocity. Thus a slip friction at least on one of the surfaces of the small and large diameters is inevitable.
The relative rotational movement of the crusher head and the main shaft is slow, but since the rotational force is very strong, the sliding friction destroys the surfaces of the crushing head and main shaft.
Damaged and roughened surface breaks the hydraulic seal, resulting in a rapid leak of the hydraulic fluid. Therefore, the inner surface of the crusher head should be coated with lubricious material or a liner of a lubricious material should be installed on it.
However, since the crusher head is exposed to extremely irregular shocks resulted from crushing of rocks or other objects, the lubricious coating or the lubricious liner can only alleviate just the surface damage due to a sliding friction, and cannot prevent sliding friction itself, thus the liner of lubricious material is also subject to gradual wear. Moreover, since a crusher head has heavy weight and large bulk, the lubricious coating or the installation of the liner of lubricious material are quite difficult and require high cost.
In order to resolve the deficiency of such conical crusher, the inventor of the present invention has filed a PCT application (WO2012/141558: hereinafter called ‘prior art 2’) of a disclosure related to a cone-shaped crusher wherein a mantle core (corresponding to the crusher head of prior art 1) has a vertically extended key groove formed on its inner circumferential surface of a cylindrical space and a main shaft has a key groove formed on its outer circumferential surface, wherein a key is inserted.
Prior art 2 allows the mantle core to move smoothly along the longitudinal direction of the main shaft, while restraining the relative rotational motion between the mantle core and the main shaft. Meanwhile, prior art 2 discloses an arrangement that a lower portion of the main shaft has a fixed crushing gap adjustment plate on which a plurality of hydraulic pressure jacks for providing hydraulic power to move the mantle core along the longitudinal direction of the main shaft is installed.
According to the prior art 2, as described above, the mantle core can suppress a relative rotation of the main shaft by the key and key groove. However, impacts resulted from crushing the rock are continuously delivered to the key and key groove, and the stresses are concentrated on them and weaken their rigidity and even impair the structural strength of the main shaft itself.